1. Field of the Invention
This invention relates to a hotmelt-adhesive fiber sheet having a superior adhesion and a good sheet-form retainability and a process for producing the sheet.
2. Description of the Related Art
Heretofore, as a sheet made of hotmelt-adhesive fibers, there have been known those obtained by conjugate-spinning polypropylene as a high melting point component and polyethylene or ethylenevinyl acetate copolymer as a low melting point component, followed by heat-treating a resulting web, thereby fixing the contact points of the fibers with each other by hotmelt-adhesion of the low melting component (Japanese patent publication No. Sho 54-44773).
Further, Japanese patent publication No. Sho 55-26203 discloses that a blend of a crystalline copolymer (propylene-butene-ethylene terpolymer) with a substantially non-crystalline ethylene-propylene random copolymer is used for regular fibers or for a low melting component of conjugate fibers, thereby improving the spinnability of a polypropylene having a low hotmelt-adhesive temperature.
However, the above prior art has raised the following drawbacks.
Since the fibers are obtained by conventional melt-spinning process, the fiber diameter is relatively large and it is difficult to obtain particularly fine fibers of 10 .mu.m or less. An oiling agent such as lubricant, etc. is required at the spinning and stretching steps, and the retainability of the sheet form is inferior, etc.
In particular, the oiling agent such as lubricant, antistatic agent, etc. used at the conventional spinning and stretching steps is indispensable at the respective steps of taking-up, cutting, secondary processing, etc., but it is economically difficult to put a post-treatment to remove the agent. Thus, there has been raised a problem that the agent remained in the final product of the fibers depress the adhesion property of the resins constituting the fibers, at the time of hotmelt-adhesion.